Clarence Lee always said if a ringed engine can maintain its rpm when leaned to peak then it can be considered run in. If the rpm drops after its peaked out then it needs more time. Older foxes and Supertigres seem to improve a lot with time. All my "older" OS's could be leaned to peak after a couple of tanks. I have never ran a model engine for more than the few minutes it takes to set the carb before it was in the air and they all run great and last years. I do think it odd when someone makes a big deal about fuel and breakin procedure, then flies from a dirt runway.